This invention relates to built, enzyme-containing liquid detergent compositions suitable for laundry or pre-soak formulations. More particularly, the invention relates to aqueous enzyme-containing liquid detergent compositions which contain one or more detergent builders and which are characterized by being stable compositions.
The formulation of stabilized enzyme-containing liquid detergent compositions has been the focus of much attention in the prior art. The desirability of incorporating enzymes into detergent compositions is primarily due to the effectiveness of proteolytic and amylolytic enzymes in decomposing proteinaceous and starchy materials found on soiled fabrics, thereby facilitating the removal of stains, such as gravy stains, blood stains, chocolate stains and the like during laundering. However, enzymatic materials suitable for laundry compositions, particularly proteolytic enzymes, are relatively expensive. Indeed, they generally are among the most expensive ingredients in a typical commercial liquid detergent composition, even though they are present in relatively minor amounts. Moreover, enzymes are known to be unstable in aqueous compositions, particularly in aqueous built detergent compositions. It is for this reason that an excess of enzymes is generally required in liquid detergent formulations to compensate for the expected loss of enzyme activity during prolonged periods of storage. The prior art is replete with suggestions for stabilizing enzyme-containing powder and liquid detergent compositions, and in particular unbuilt liquid compositions by the use of various materials which are incorporated into the composition to function as enzyme stabilizers.
In the case of liquid detergent compositions containing a phosphate builder, the problem of enzyme instability is particularly acute. This is primarily because phosphate detergent builders have a destabilizing effect on enzymes, even in compositions containing enzyme stabilizers which are otherwise effective in unbuilt formulations. Moreover, the incorporation of a phosphate builder into a liquid detergent composition poses an additional problem, namely the ability to form a stable single-phase composition; the solubility of sodium tripolyphosphate, for example, being relatively limited in aqueous compositions, and especially in the presence of anionic detergents.
Heavy duty aqueous liquid detergents with greater than 5% sodium tripolyphosphate (TPP) are relatively new. The stabilization of enzymes in this type of system is more difficult than with powders containing more than 5% sodium tripolyphosphate (TPP). While it is possible to reduce the pH to improve enzyme stability this negates to some extent the benefit of the builders. The stabilized enzyme system of the present invention provides enzyme stability even at relatively high pH's, up to pH 10-11. The higher pH's, e.g. pH 10-11, are known to give better detergency and are preferred. Reducing the detergent composition pH, e.g. to pH 7.5 to 9.5 can increase the stability of the enzyme, but reduces suds life and the benefits of the builder, i.e. detergency.